Waste water treatment systems used in the industry generally include, but are not limited to, the following treatment processes: grit removal, fine screening, flow equalization and primary clarification. The typical treatment processes are dependent on the velocity at which the waste water is moving through the system. Waste water, however, is not produced continually by humans, but instead is created in batch type processes, such as showering, flushing a toilet or operating a washing machine. Such water consumptive activities are generally repetitive resulting in daily, weekly, monthly and yearly diurnal flow patterns for a specific waste water treatment system.
Grit removal is generally performed in a grit chamber/channel which is velocity sensitive, having a required design velocity of 1.0 to 3.0 feet per second. The most common methods to remove grit are by reducing the velocity of the influent flow so that the grit settles out, or utilizing a circular channel/tank. The circular channel/tank is a hydro-cyclone that causes the grit to settle in a sump, separating the organics from the grit so that they can move forward to the biological processes. The grit is then pumped out of the sump to a grit washer and then discharged to a dumpster for disposal at a landfill. This technology is subject to a large variation in flows.
Fine screening is typically accomplished by placing a screen in an influent channel. The influent channel must have a minimum velocity of 1.25 feet per second to keep solids from settling out in the channel and a maximum velocity of 3.0 feet per second to keep solids from being forced through the screen. Such a flow is difficult to achieve due to the large variation in diurnal and pumped flow patterns.
Typical primary clarifiers are also velocity sensitive with the heavy solids going to the base of the clarifier where they are pumped to a digester, the floatable solids, grease and scum being trapped and skimmed off the surface and the neutral buoyant solids/clarified wastewater exits the basin via an effluent weir. Primary clarifiers are typically large tanks designed for gravity settling and may include electrical drives, flights and chains, rack arms and paddles or suction tubes, and sludge pumps.
Flow equalization typically occurs in a separate tank. The flow at the waste water plant is subject to travel times in the collection system, collection system design and pump station sizing. In general, larger collection systems use pump stations to lift the waste water to the treatment facility. The pumps are typically placed on variable-frequency drives in an attempt to provide a consistent uniform flow. The system of variable-frequency drives and pumps, however, fails in low and high flow conditions. The pumps must be designed for peak hourly flows and have minimum turn down capabilities.
These treatments and processes generally each require their own mechanical equipment and supporting infrastructure resulting in higher capital costs to develop the system, increased maintenance, and higher energy costs. Further, the necessary supporting infrastructure requires a large amount of space to develop a traditional waste water treatment system. Thus, there is a need to develop a waste water treatment system where the treatment processes are performed in a single tank, which uses less energy, requires fewer construction materials and less mechanical maintenance, and takes up less space, while at the same time offering improved BOD reduction and a uniform flow to downstream processes.